我們透過大強子對撞機中的ATLAS探測器量測與一般物質有交互作用的物質的特性，分析某模型預測中，較不能與一般物質有交互作用之物質的存在與否，對於其背景事件的研究將在本篇文章中提及。

We make use of ATLAS detector in the Large Hadron Collider to measure the physical quantity of matters that interact with other matters. This measurement are used to analyze the existence of a predicted invisible particle by a certain model. The studies of the background estimation are stated in this article.

1. Introduction............................1
2. The ATLAS Detector......................4
3. Object Selection and Reconstruction.....8
4. Event Selection.........................15
5. Study on the Background Estimation......20
6. Results of monoHbb Analysis.............27
7. Conclusion..............................31
Bibliography...............................32

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